I DESCRIPTION (provided by applicant): The Exercise Core Facility will provide two different approaches, voluntary wheel running and low-frequency tonic pacing of the motor nerve, to augment contractile activity in muscles of intact mice. Both of these procedures are associated with changes in endogenous gene expression consistent with fiber type transformation. These procedures have previously been developed, tested and successfully used in wild type and transgenic animals under the supervision of Dr. Bassel-Duby at UT Southwestern. In addition, we will perform studies on isolated skeletal muscle function to study the isometric and isotonic contractile function of mouse skeletal muscle.